Rotatable filters of this kind are described, a.o., in the Patent No. SE-C-8305817-2 (corresponding to EP-B1-0160069 and US-A-4 634 529). As is well known to those skilled in the art there is a disadvantage occurring in such filters which is usually called re-wetting or "backwash", meaning that the filtrate, which has not yet had time to leave the interior of a filter section before the sub-pressure in the discharge conduit ceases, flows back again through the filter cloth. It is thus desirable that the interior volume of a filter section be kept as small as possible, so that the least possible quantity of filtrate will be able to flow back. To decrease the volume by making the space between the disk shaped elements small results in problems in strength, since a filter section is subjected to both bending and torsion, as well as flow problems, since a relatively large area is required at the outlet end of the section to permit the discharge of filtrate.